U.S. patent number 4,201,660 [Application Number 05/875,034] was granted by the patent office on 1980-05-06 for process for the separation of mixtures of various hydrocarbon compounds.
This patent grant is currently assigned to Studiengesellschaft Kohle mbH. Invention is credited to Kurt Zosel.
United States Patent |
4,201,660 |
Zosel |
* May 6, 1980 |
**Please see images for:
( Certificate of Correction ) ** |
Process for the separation of mixtures of various hydrocarbon
compounds
Abstract
A process for separating petroleum distillation residues into a
lower boiling fraction and a higher boiling fraction. The
separation is effected with the aid of a process gas under
super-critical conditions of temperature and pressure such that the
gas selectively takes up the lower boiling fraction. By suitable
selection of the gas, the process can be carried out at relatively
low temperature, and with low input energy requirements when
performed with recycling of the process gas.
Inventors: |
Zosel; Kurt (Oberhausen,
DE) |
Assignee: |
Studiengesellschaft Kohle mbH
(Muhlmann, DE)
|
[*] Notice: |
The portion of the term of this patent
subsequent to July 13, 1993 has been disclaimed. |
Family
ID: |
3589290 |
Appl.
No.: |
05/875,034 |
Filed: |
February 3, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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808946 |
Jun 22, 1977 |
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734562 |
Oct 21, 1976 |
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658657 |
Feb 17, 1976 |
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492100 |
Jul 26, 1974 |
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113025 |
Feb 5, 1971 |
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718959 |
Apr 4, 1968 |
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476106 |
Jul 30, 1965 |
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Foreign Application Priority Data
Current U.S.
Class: |
208/86; 208/251R;
208/308; 208/309 |
Current CPC
Class: |
B01D
3/00 (20130101); B01D 3/343 (20130101); B01D
11/0203 (20130101); B01D 12/00 (20130101); C10G
21/003 (20130101); C10G 31/00 (20130101); B01D
11/0407 (20130101) |
Current International
Class: |
B01D
11/02 (20060101); B01D 12/00 (20060101); B01D
11/04 (20060101); B01D 3/34 (20060101); B01D
3/00 (20060101); C10G 31/00 (20060101); C10G
21/00 (20060101); B01D 017/00 (); C10G
021/14 () |
Field of
Search: |
;208/251R,308,309,86 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Zhuze, "Maslob. Zhir. Promst.", 24, 34-37 (1958)..
|
Primary Examiner: Levine; Herbert
Attorney, Agent or Firm: Sprung, Felfe, Horn, Lynch &
Kramer
Parent Case Text
This is a continuation of Ser. No. 808,946 filed June 22, 1977;
which is a continuation of Ser. No. 734,562 filed Oct. 21, 1976;
which is a continuation of Ser. No. 658,657 filed Feb. 17, 1976;
which is a continuation of Ser. No. 492,100 filed July 26, 1974;
which is a continuation of Ser. No. 113,025 filed Feb. 5, 1971;
which is a continuation of Ser. No. 718,959 filed Apr. 4, 1968;
which is a continuation of Ser. No. 476,106 filed July 30, 1965 and
which are all now abandoned.
Claims
What is claimed is:
1. A process for the separation of petroleum distillation residues
containing lower boiling fraction and higher boiling fraction,
which comprises the steps:
(a) contacting said residue in liquid state with a process gas
under super-critical conditions of temperature and pressure of the
gas such that the gas will take up at least a portion of said
mixture in a quantity varying inversely with said temperature, and
effecting said contacting in a manner so that this occurs, said gas
having a critical temperature of 90.degree.-250.degree. C. and
being inert to the distillation residue, so that a portion of the
lower boiling fraction is taken up by the process gas, whereby
there is formed a gas phase containing process gas and lower
boiling fraction taken up by the process gas, and a liquid hase
containing higher boiling fraction of said distillation residue,
said contacting being at a temperature up to 100.degree. C. above
the critical temperature,
(b) separating the gas phase from the liquid phase, while still
maintaining super-critical conditions as aforesaid, thereafter
(c) condensing at least part of the lower boiling fraction from the
gas phase by reducing the pressure,
(d) separating condensed lower boiling fraction from the two phase
mixture resulting from the condensation,
(e) after separating the lower boiling fraction, cooling the
process gas resulting from the separation to liquefy the process
gas,
(f) pressurizing the liquefied process gas to the super-critical
pressure employed in step (a),
(g) heating the pressurized liquefied process gas to the
super-critical temperature employed in step (a) to convert it to
process gas at the super-critical temperature and pressure used in
step (a), in said heating supplying only energy to raise the
temperature,
(h) employing the process gas produced in step (g) in the
contacting of step (a).
2. A process as claimed in claim 1 in which the process gas is of
the group C.sub.3 to C.sub.6 hydrocarbons.
3. A process as claimed in claim 1 in which the process gas is of
the group C.sub.3 and C.sub.4 hydrocarbons.
4. Process according to claim 1, wherein propane is the process
gas.
5. Process according to claim 1 for the separation of petroleum in
which low boiling fraction is condensed from the gas phase by
reducing the pressure to a value sufficiently high to enable the
process gas to be liquefied by cooling to room temperature and
effecting said liquefying of the process gas by cooling to a
temperature not below room temperature.
6. Process according to claim 1, wherein said heating in step (g)
comprises heat exchange with the gas phase resulting from said
contacting and heat exchange with the condensate free process
gas.
7. Process according to claim 5, wherein said heating in step (g)
comprises heat exchange with the gas phase resulting from said
contacting and heat exchange with the condensate free process
gas.
8. A process as claimed in claim 5 in which the following operating
conditions are used: contacting, 100.degree. to 150.degree. C.,
pressures of at least 100 atmospheres; separating, release of
pressure to 30 to 40 atmospheres; liquefaction by cooling to
20.degree. to 30.degree. C.
9. A process according to claim 8, wherein the contacting operating
pressure is 100-200 atmospheres.
10. Process according to claim 1, wherein said petroleum
distillation residue contains an appreciable amount of vanadium
compounds, said lower boiling fraction taken up in the gas phase
containing not more than a trace of vanadium.
11. Process according to claim 1, wherein, in the separation of the
low boiling fraction, the pressure is reduced to below the critical
pressure.
12. Process according to claim 5, wherein, in the separation of the
low boiling fraction, the pressure is reduced to below the critical
pressure.
13. Process according to claim 1, wherein the process gas is
propane, the contacting temperature is 100.degree. to 150.degree.
C., contacting pressure is 100 to 150 atmospheres, separating by
releasing of pressure to 30 to 40 atoms.
14. Process according to claim 13, wherein liquefaction is by
cooling to 20.degree. to 30.degree. C.
15. Process according to claim 1, in which the process gas is of
the group C.sub.3 and C.sub.4 hydrocarbons, the contacting is at a
temperature up to 100.degree. C. above the critical temperature,
and low boiling fraction is condensed from the gas phase by
reducing the pressure to a value sufficiently high to enable the
process gas to be liquefied by cooling to room temperature and
effecting said liquefying of the process gas by cooling to a
temperature not below room temperature.
16. A process for the separation of petroleum distillation residues
containing lower boiling fraction and higher boiling fraction,
which comprises the steps:
(a) contacting said residue in liquid state with a process gas
under super-critical conditions of temperature and pressure of the
gas such that the gas will take up at least a portion of said
mixture in a quantity varying inversely with said temperature, and
effecting said contacting in a manner so that this occurs, said gas
having a critical temperature of 90.degree.-250.degree. C. and
being inert to the distillation residue, so that a portion of the
lower boiling fraction is taken up by the process gas, whereby
there is formed a gas phase containing process gas and lower
boiling fraction taken up by the process gas, and a liquid phase
containing higher boiling fraction of said distillation residue,
said contacting being at a temperature up to 100.degree. C. above
the critical temperature,
(b) separating the gas phase from the liquid phase, while still
maintaining super-critical conditions as aforesaid, thereafter
(c) condensing at least part of the lower boiling fraction from the
gas phase by reducing the pressure to a value sufficiently high to
enable the process gas to be liquefied by cooling to room
temperature,
(d) separating condensed lower boiling fraction from the two phase
mixture resulting from the condensation,
(e) after separating the lower boiling fraction, cooling the
process gas resulting from the separation to liquefy the process
gas,
(f) compressing the liquefied process gas to the super-critical
pressure employed in step (a),
(g) heating the compressed liquefied process gas to the
super-critical temperature employed in step (a) to convert it to
process gas at the super-critical temperature and pressure used in
step (a),
(h) employing the process gas produced in step (g) in the
contacting of step (a).
17. A process according to claim 1, and hydrocracking the separated
lower boiling fraction of step (d).
18. A process for the separation of petroleum distillation residues
containing lower boiling fraction and higher boiling fraction,
which comprises the steps:
(a) contacting said residue in liquid state with a process gas
under super-critical conditions of temperature and pressure of the
gas such that the gas will take up at least a portion of said
mixture in a quantity varying inversely with said temperature, said
gas having a critical temperature of 90.degree.-250.degree. C. and
being inert to the distillation residue, so that a portion of the
lower boiling fraction is taken up by the process gas, whereby
there is formed a gas phase containing process gas and lower
boiling fraction taken up by the process gas, and a liquid phase
containing higher boiling fraction of said distillation residue,
said contacting being at a temperature up to 100.degree. C. above
the critical temperature,
(b) separating the gas phase from the liquid phase, while still
maintaining super-critical conditions as aforesaid, and
(c) following step (b), separating at least part of the lower
boiling fraction from the process gas.
19. A process for the separation of petroleum residues containing
lower boiling fraction and higher boiling fraction, which comprises
the steps:
(a) contacting said residue in liquid state with a process gas
under super-critical conditions of temperature and pressure of the
gas such that the gas will take up at least a portion of said
mixture in a quantity varying inversely with said temperature, and
effecting said contacting in a manner so that this occurs, said gas
having a critical temperature of 90.degree.-250.degree. C. and
being inert to the distillation residue, so that a portion of the
lower boiling fraction is taken up by the process gas, whereby
there is formed a gas phase containing process gas and lower
boiling fraction taken up by the process gas, and a liquid phase
containing higher boiling fraction of said distillation residue,
said contacting being at a temperature up to 100.degree. C. above
the critical temperature.
(b) separating the gas phase from the liquid phase, while still
maintaining super-critical conditions as aforesaid, and
(c) following step (b), separating at least part of the lower
boiling fraction from the process gas.
20. A process for the separation of petroleum distillation residues
containing lower boiling fraction and higher boiling fraction,
which comprises the steps:
(a) contacting said residue in liquid state with a process gas
under super-critical conditions of temperature and pressure of the
gas such that the gas will take up at least a portion of said
mixture in a quantity varying inversely with said temperature, and
effecting said contacting in a manner so that this occurs, said gas
having a critical temperature of 90.degree.-250.degree. C. and
being inert to the distillation residue, so that a portion of the
lower boiling fraction is taken up by the process gas, whereby
there is formed a gas phase containing process gas and lower
boiling fraction taken up by the process gas, and a liquid phase
containing higher boiling fraction of said distillation residue,
said contacting being at a temperature up to 100.degree. C. above
the critical temperature, and
(b) separating the gas phase from the liquid phase, while still
maintaining super-critical conditions as aforesaid, and
(c) following step (b), condensing at least part of the lower
boiling fraction from the gas phase by reducing the pressure, or
increasing the temperature, or reducing the pressure and increasing
the temperature, to condense lower boiling fraction and provide a
two phase mixture of condensed lower boiling fraction and process
gas.
21. A process as claimed in claim 20, in which the process gas is
of the group C.sub.3 to C.sub.6 hydrocarbons.
22. A process as claimed in claim 20, in which the process gas is
of the group C.sub.3 and C.sub.4 hydrocarbons.
23. A process according to claim 20, wherein the gas is propane or
propylene.
24. A process according to claim 20, wherein the gas is
propane.
25. A process as claimed in claim 20, in which:
(d) said condensed lower boiling fraction is separated from the two
phase mixture thereof with process gas,
(e) following said separation in step (d), the process gas is
substantially all recycled to step (a).
26. A process according to claim 20, in which:
(d) said condensation is effected by reducing the pressure,
(e) separating condensed lower boiling fraction from the two phase
mixture resulting from the condensation,
(f) after separating the lower boiling fraction, cooling the
process gas resulting from said separation to liquefy the process
gas,
(g) compressing the liquefied process gas to the super-critical
pressure employed in step (a).
(h) recycling the compressed process gas to step (a).
27. A process as claimed in claim 20, in which:
(d) said condensation is effected by reducing the pressure,
(e) separating condensed lower boiling fraction from the two phase
mixture resulting from the condensation,
(f) after separating the lower boiling fraction, cooling the
process gas resulting from said separation to liquefy the process
gas,
(g) compressing the liquefied process gas to the super-critical
pressure employed in step (a),
(h) heating the compressed liquefied process gas to the
super-critical temperature employed in step (a) to convert it to
process gas at the super-critical temperature and pressure used in
step (a),
(i) employing the process gas produced in step (b) in the
contacting of step (a).
28. A process as claimed in claim 27, in which the process gas is
of the group C.sub.3 to C.sub.6 hydrocarbons.
29. A process as claimed in claim 27 in which the process gas is of
the group C.sub.3 and C.sub.4 hydrocarbons.
30. A process for the separation of petroleum distillation residues
containing lower boiling fraction and higher boiling fraction,
which comprises the steps:
(a) contacting said residue in liquid state with a process gas
under super-critical conditions of temperature and pressure of the
gas such that the gas will take up at least a portion of said
mixture in a quantity varying inversely with said temperature, and
effecting said contacting in a manner so that this occurs, said gas
having a critical temperature of 90.degree.-250.degree. C. and
being inert to the distillation residue, so that a major portion of
the lower boiling fraction is taken up by the process gas, whereby
there is formed a gas phase containing process gas and a lower
boiling fraction taken up by the process gas, and a liquid phase
containing higher boiling fraction of said distillation residue,
said contacting being at a temperature up to 100.degree. C. above
the critical temperature, and
(b) separating the gas phase from the liquid phase, while still
maintaining super-critical conditions as aforesaid.
31. A process according to claim 30, comprising the steps of
introducing the distillation residue and the process gas
continuously into a contacting zone for said contacting and then
into a separating zone for said separating so that both the process
gas and distillation residue pass in a unidirectional stream
through said zones, and intimately mixing the process gas and
distillation residue in said contacting zone, and stilling said
mixture prior to introduction into the separating zone to
facilitate said separation.
32. A process as claimed in claim 31, in which the temperature of
contacting is up to 100.degree. C. above the critical temperature
of the process gas.
33. A process according to claim 30, the low boiling fraction is
condensed from the separated gas phase by reducing the pressure to
a sub-critical value sufficiently high to enable the process gas to
be liquified by cooling to room temperature.
34. A process as claimed in claim 33, in which propane is used as
the process gas.
35. A process according to claim 33, wherein said condensation
provides a two phase mixture of condensed low boiling fraction and
process gas, said condensate is separated from the two phase
mixture and the resulting condensate-free process gas is liquified
by cooling and thereafter compressed to the pressure employed in
the contacting, and is thereafter heated to the temperature
employed in said contacting, said heating including heat exchange
with the gas phase resulting from said contacting and said
condensate-free process gas.
36. A process as claimed in claim 33, in which the following
operating conditions are used
contacting: 100.degree. to 150.degree. C., pressures of at least
100 atmospheres,
separating: release of pressure to 30 to 40 atmospheres,
liquefaction by cooling to 20.degree. to 30.degree. C.
37. A process according to claim 36, wherein the contacting
operating pressure is 100-200 atmospheres.
38. A process as claimed in claim 31, in which the stilled mixture
passes obliquely downward into the separation zone from which the
gas phase is removed at the top while the liquid phase flows
downward and is discharged from the separating zone.
39. A process as claimed in claim 38, in which the temperatures of
contacting is up to 50.degree. C. above the critical temperature of
the process gas.
40. In a process of catalytic cracking of a petroleum fraction by
hydrogenation, the improvement which comprises utilizing as said
fraction, material separated by the process of claim 1 from
petroleum distillation residue as a lower boiling fraction
thereof.
41. Process according to claim 18, wherein said petroleum
distillation residue contains an appreciable amount of vanadium
compounds, said lower boiling fraction taken up in the gas phase
containing not more than a trace of vanadium.
42. Process according to claim 41, condensing at least part of the
low boiling fraction from the gas phase by reducing the pressure or
increasing the temperature or reducing the pressure and increasing
the temperature, to condense lower boiling fraction and provide a
two phase mixture of condensed lower boiling fraction and process
gas, separating condensed lower boiling fraction from the two phase
mixture, and recycling process gas resulting from the separation of
the two phase mixture to said contacting of residue and process
gas.
Description
This invention relates to a new process for the separation of
mixtures of various hydrocarbon compounds and is especially
suitable for the separation of petroleum distillation residues or
other higher boiling hydrocarbon materials. The new process can
above all be used advantageously for the deasphalting of petroleum
distillation residues for the purpose of obtaining purified
hydrocarbon fractions which are free from unwanted compounds and
which can then be subjected to further processing such as splitting
by hydrogenation.
In industry, and especially in the course of petroleum processes,
large quantities of higher boiling distillation residues are
obtained daily which either cannot be worked up economically, at
all, or only under difficult conditions, e.g., during the usual
vacuum distillation or known extraction processes. A special
problem in this field is the deasphalting of petroleum residues
from atmospheric or vacuum distillation. It is known that the
highest boiling constituents of the crude oil present in these
residues, and especially the asphaltenes contained therein, must be
removed to a large extent if the hydrocarbon compounds of these
residues are to be subjected to further treatment, for example to
catalytic decomposition by hydrogenation. The working up of higher
boiling hydrocarbon compounds of petroleum to obtain petroleum and
middle oil region is also nowadays of value and importance.
In practice, purification of such distillation residues has
previously been carried out either by vacuum distillation or by an
extraction process such as the known extraction process with liquid
propane. Both methods are relatively costly and involved. The
invention provides especially in this case a new method for simple,
economic purification of such distillation residues or other higher
boiling hydrocarbon materials.
In an earlier patent application (patent application Ser. No.
359,680 filed Apr. 4, 1964, now abandoned replaced by Ser. No.
880,475 filed Dec. 9, 1969), now U.S. Pat. No. 3,969,196, a new
separating process for separating mixtures containing organic
compounds has been described which is characterized in that the
mixture is treated with a gas which is under super-critical
conditions of temperature and of pressure. At least a part of the
organic compounds are taken up in the super-critical gas phase and,
if the mixture of substances is not completely taken up, the
charged gas is separated under super-critical conditions from the
part of the mixture that has not been taken up and the compounds
taken up in the super-critical gas phase are recovered. This new
process is based on two important principles; these are, firstly,
that it has been found that super-critical gas phases are in
principle capable of taking up certain classes of compounds, e.g.,
organic compounds, in large quantities and, secondly, on the
finding that this "uptake capacity" in the super-critical gas is
not the same for all compounds but depends on the constitution of
the compound. The tendency to enter the super-critical phase
therefore differs for different compounds. The greater the uptake
capacity of a compound in the super-critical gas, the more rapidly
will it go over into the super-critical gas under otherwise
comparable reaction conditions, and the greater will be the
proportion taken up in a given quantity of the super-critical gas
phase. Consequently, when treating a mixture of substances
containing constituents that are easily taken up and constituents
that are less easily taken up, the constituents more easily taken
up are accordingly taken up preferentially by the super-critical
gas phase so that they can thus be separated from the constituents
that are less easily taken up. It has also been found, inter alia,
the molecular weight, which is also reflected in the boiling point,
helps to determine the extent to which a compound will be taken up
in the super-critical gas phase, the lower boiling compounds of a
homologous series being as a rule more easily taken up than the
higher boiling compounds of that series.
In said Ser. Nos. 359,680 and 880,475 it has already been pointed
out that the new process is especially suitable for the treatment
of petroleum and petroleum fractions or comparable hydrocarbon
mixtures. The process according to the invention, on the other
hand, relates to a particularly economic and important combination
of individual features of a process for the working up of petroleum
fractions or comparable hydrocarbon mixtures and is especially
suitable for economic deasphalting of distillation residues from
petroleum distillation.
The present invention provides a separation process, in particular
for the deasphalting of petroleum distillation residues or other
higher boiling hydrocarbon materials, in which the starting
material which is to be separated is treated with a gas which is
under super-critical conditions of temperature and of pressure and
which has a critical temperature in the range of 90.degree. to
250.degree. C., a part of the starting material is taken up into
the over-critical phase, the charged gas phase is separated from
the part which has not been taken up and the part of the starting
mixture which has been taken up into the gas is recovered by
release of pressure and/or increase of temperature. According to
the invention, it is preferred to use C.sub.3 to C.sub.6
hydrocarbon compounds as the super-critical gas phase, and the
process is advantageously carried out with C.sub.3 and/or C.sub.4
hydrocarbon compounds. The most suitable hydrocarbon for the
process according to the invention is propane, but propylene is
also particularly suitable.
The process according to the invention is thus characterized by a
combination in the choice of certain super-critical gases from the
large group of gaseous phase which can in principle be used for the
new separation process in conjunction with certain higher boiling
mixtures of substances which are to be separated. The choice of the
super-critical gases is connected with the choice of a starting
mixture which in particular cannot be decomposed into its
components by simple atmospheric distillation. The reason for this
is that it has been found that it is precisely for such high
boiling hydrocarbon mixtures that the new separation process is
more economical in installation and procedure than the separation
and purification processes hitherto known. The costs of
installation and operation both of a vacuum distillation plant and
of an extraction, for example with liquid propane, are considerably
higher than the corresponding costs for the process according to
the invention.
It is precisely to this question of economy of the new process that
the development according to the invention makes an important
further contribution to the new process, the basic principles of
which have been described in the above mentioned earlier patents.
These are as follows:
The gas phase which is charged under super-critical conditions with
a part of the mixture to be separated and is separated from the
remainder of the mixture can be at least partly freed from the
compounds it has taken up by increase in temperature or by release
of pressure since the uptake capacity of the compounds in the
super-critical gas drops with increasing temperature of diminishing
pressure. Practically complete removal of the compounds taken up is
achieved if, for example, the pressure in the gas phase is dropped
sufficiently far below the critical pressure. If the compounds
taken up are then obtained in the liquid or solid phase, the gas
stream which has been freed from its charge can easily be separated
and must then be returned to the charging stage operated under
super-critical conditions. Thus, if, for example, the compounds
taken up are precipitated at least partly by a reduction in
pressure, then the gas stream from which these compounds have been
removed must again be raised to the super-critical pressure in the
charging stage before it can be used again. It will thus be
necessary to compress relatively large quantities of gas, and it is
well known that this requires extensive installations which are not
economical to run.
According to one important feature of the invention presented here,
the process described in the earlier patents is decisively improved
especially in this respect since according to the invention
liquefaction of the gas phase is interposed between the stage of
discharging the charged super-critical gas stream by release of
pressure and the stage of renewed compression of the discharged gas
stream to the super-critical operating pressure in the charging
stage. The advantage of this procedure is obvious. It is very much
easier and less expensive to compress a given quantity of material
in the liquid phase from the low discharging pressures to the
higher super-critical operating pressures of the charging stage
than to bring the same quantity of material in the gaseous phase
from the lower to the higher pressures.
According to the invention, the improvement described can simply be
achieved by cooling the gas stream discharged in the desired manner
to such an extent that liquefaction takes place. Working up the
charged, super-critical gas stream separated from the remainder of
the starting material thus takes place in two stages. In the first
stage the pressure is lowered, preferably at a super-critical
temperature in order to exclude the possibility of unwanted
liquefaction of the gas phase, so far below the critical pressure
that the constituents taken up are precipitated as desired. The
compounds which had been taken up, which according to the invention
are now obtained in a separate phase, are separated from the now
discharged gas stream. The temperature of this discharged gas
stream is then lowered to such an extent below the critical
temperature that the gas stream liquefies. The liquid stream thus
obtained is again pressurized to the super-critical operating
pressure of the charging stage and the liquid thus pressurized is
heated to the super-critical operating temperature. Compression of
large quantities of gas is in this way avoided by simple means.
Another feature which renders the new process more economical is
that the transition from the sub-critical into the super-critical
state does not involve any significant additional energy changes
such, for example, as the latent energy of evaporation required for
the transition from the liquid phase into the gaseous phase under
sub-critical conditions. For heating the recompressed liquid stream
to temperatures in the region of the super-critical operating
temperature it is therefore only necessary to provide the energy
actually necessary for the increase in temperature but not any
additional energy.
Liquefaction of the discharged gas stream can be carried out
especially economically and simply if simple conventional cooling
devices are sufficiently for bringing about the desired
liquefaction, in other words especially if the gas need not be
cooled below room temperature. According to the invention it is
thus especially preferred, in the discharge of the gaseous phase by
release of pressure to sub-critical values, to maintain
sufficiently high pressures to enable the gas to liquefy by cooling
to room temperature. This is what is meant by the choice of gas
phases according to the invention. Propane (critical temperature
above 95.degree. C.) lies for example at the lower limit of the
region for critical temperatures of the gases used according to the
invention. Since at the same time the critical pressure of propane
is in the region of 43 atmospheres, satisfactory separation of
compounds taken up can be ensured by dropping the pressure to 30 to
40 atmospheres during the pressure release stage. At the same time,
these pressures are still sufficiently high to enable propane to
liquefy when cooled to temperatures in the region of 20 to
30.degree. C., so that recompression can be carried out in the
simple manner described above. It will be obvious that the features
of the invention can be utilized in analogous manner for compounds
having higher critical temperatures, for example when C.sub.4
hydrocarbons are used which accordingly condense at higher
temperatures. This is all the more so the higher the critical
temperatures are and hence the higher the condensation points of
the gas phases used.
Nevertheless, the C.sub.3 hydrocarbons as well as the C.sub.4
hydrocarbons have a preferential position in the process of the
invention since they cannot only be condensed to the liquid phase
by being cooled to room temperature but they also have relatively
low critical temperatures so that it is possible to work at
relatively low temperatures during the charging stage. It is
especially the working up of petroleum distillation residues which
it is advantageous to carry out in this manner since the charging
can be carried out at a temperature at which thermal cracking of
constituents of the distillation residue is practically impossible.
Herein lies an important advantage, e.g. also in comparison with
vacuum distillation since it is thus possible to prevent the
occurrence of unwanted breakdown products of lower boiling ranges
in the desired fractions of the residue.
It has further been found that charging can also be carried out in
a very simple manner. According to the invention, it is preferred,
to send the starting material which is to be separated, in other
words for example the distillation residue and the super-critical
gas stream, in a unidirectional current through a charging zone
under the operating conditions of the charging stage. In this
procedure, intimate contact between the gas phase and the starting
material to be separated is first ensured. This can be effected,
for example, by filling the charging zone with filling bodies and
passing the mixture of gas phase and starting mixture to be
separated through this zone. The uptake of the compounds to be
separated in the super-critical gas phase takes place rapidly and
it becoms advisable after only a short time to still this mixture
of super-critical gas and material to be separated. This can easily
be done by ensuring that the stream does not encounter any further
obstructions which would lead to whirling up of the stream, and if
desired, baffle plates may be arranged in the direction of the
stream to convert the turbulent flow into a laminar fow. During
this phase of pacifying the stream, the charged gas phase and the
remainder of the starting material separate from each other, the
starting material which has not been taken up being usually present
as the lower liquid phase. In this form, the two phases of the
stream of product can easily be branched into different paths to
ensure the desired rapid and sure separation. Thus it may be
advantageous to conduct the stilled, laminar stream of mixture
obliquely downwards into the separating zone in which the charged
gas phase is removed at the top while the constituents of the
mixture which has not been taken up flow down under the effect of
gravity.
According to the invention, it is especially preferred if the
super-critical temperatures employed in the chargng and separating
zone are such that the starting mixture and preferably also those
constituents of the starting mixture that have not been taken up
are present in the liquid phase. Further, in accordance with the
general information given in the above-mentioned earlier patents,
it is preferred to work in the temperature region of up to
100.degree. C. above the critical temperature of the gas employed,
preferably in the temperature region of up to 50.degree. C. above
the critical temperature. The choice of super-critical gas to be
used in any particular case results from the combination of all
these conditions and it is found that the use of C.sub.3 or C.sub.4
hydrocarbons, especially propane, again provides special advantages
particularly for the treatment of petroleum distillation residues
and comparable high boiling hydrocarbon materials. With propane,
which has a critical temperature of about 95.degree. C., it is
possible to work e.g. in a temperature region of 100.degree. to
150.degree. C. In this temperature region, distillation residues
and the products of the process are sufficiently fluid.
The otherwise generally valid rules for carrying out separations
with the aid of super-critical gases are indicated in said Ser.
Nos. 359,680 and 800,475 which are, of course, also applicable
here. Thus the larger the quantities of compounds that are to be
taken up from the mixture per unit quantity of super-critical gas,
the higher will be the pressures employed during the procedure of
charging above the critical pressure. Using propane as example, it
will be explained with the aid of actual values that economic
conditions can easily be obtained. Thus when working with propane
at pressures of 100 to 150 atmospheres and at temperatures in the
region of 100.degree. to 150.degree. C., two parts by weight of the
super-critical gas are sufficient for one part by weight of the
distillation residue to obtain practically sufficient splitting up
of the residue. It is, of course, also possible to employ other
proportions. These figures are intended merely to demonstrate the
effectiveness of the new process.
In any particular case, a combination of operating pressure,
temperature and ratio of gas phase to residue will be chosen which
leads to the desired distribution of the mixture to be separated.
Above all, the combination of these factors is used to determine
the quantity which is not taken up from the mixture to be
separated. It is obvious that in this way it is possible to
separate the asphaltene-containing high boiling constituents in any
desired proportion from the valuable constituents of the starting
material.
The data given below concerning the volume-time yields of such a
process is also by way of exemplification. It has been found that
up to 10 or more parts of distillation residue per unit volume of
charging zone and separating zone can easily be put through per
hour. Very high rates of throughput can thus be achieved with
relatively small separation apparatus, especially in comparison
with the process of vacuum distillation.
The super-critical gases used should be inert to the mixture to be
separated under the conditions of the process.
In the accompanying drawing:
FIG. 1 is a flow sheet for an embodiment of the process of the
invention, illustrating the construction of some of the equipment
utilized; and
FIG. 2 is a cross-sectional view taken along line 2--2 in FIG.
1.
A working cycle for carrying out the process according to the
invention is illustrated diagrammatically in the accompanying flow
sheet. The charging and separation apparatus (1) consists of a
middle portion, which is here shown to be spherical, a separation
zone, an upwardly directed arm which opens into the side of the
zone, a charging zone and a discharge outlet which is attached at
the bottom and which serves to receive the residue which has not
been taken up from the mixture to be separated and which it is
conducted from there into a storage tank (7) through the pressure
reducing valve (6). The arm serving as charging zone of the part
(1) of the apparatus is filled in its upper part with small filling
bodies and in its lower part with larger filling bodies. Just
before the transition into the spherical separation part, a tubular
section is provided which contains vertical baffle plates to still
the mixture, i.e., to ensure the desired laminar flow of the
mixture conducted through the charging zone. The spherical
separation member is separated in the middle by a perforated plate,
and filling bodies are arranged above this plate. The downwardly
directed receiving tube for the residue which has not been taken up
from the mixture to be separated has no installations. The whole
arrangement is kept at the desired operating temperature by a
heating apparatus (not shown in the drawing).
The material to be separated, a distillation residue containing low
and high boiling fractions, preferably pre-heated to the operating
temperature, is continuously supplied to the charging zone through
the pipe (2). At the same time, the super-critical carrier gas,
i.e., the process gas, which is also preferably preheated to the
operating temperature, is continuously conducted into the
contacting zone through (3) and flows in the same direction as the
starting mixture to be separated, first in a turbulent flow and
later in a laminar flow into the spherical separationg part. The
starting material is in liquid state in the contacting zone. On
passing through the layer of filling bodies, the carrier gas which
is in the super-critical state becomes charged with the
constituents to be separated and is continuously removed through
the pipe (4). The component which has not been taken up by the
super-critical gas phase flows as a liquid into the lower pipe and
is removed from there through the pipe (5) and the discharge valve
(6). The carrier gas removed through (4) is first conducted into
the heat exchanger (8) and then enters the intermediate container
(10) through the reducing valve (9). In the reducing valve (9), the
pressure is reduced to the sub-critical region. During this
operation, the carrier gas becomes separated from the constituents
it has taken up by reason of condensation of these constituents
(low boiling fraction), and these constituents are deposited at the
bottom of the container (10) and removed into the storage container
(12) through the valve (11). The reducing valve (9) and the
separation container (10) are surrounded by the heating jacket (18)
which ensures that sufficiently high temperatures are maintained
during this stage of the process to enable the compounds deposited
in (10) to be easily separated from the discharge gas phase.
The carrier gas freed from the constituents previously taken up by
it is removed through (13) and on passing through the heat
exchanger (14) is sufficiently cooled to liquefy. This liquefied
gas stream is again raised to the operating pressure in the
charging and separating apparatus (1) by means of the liquid pump.
The liquid stream again flows under the operating pressure to the
heat exchanger (14) but in the reverse direction and subsequently
to the heat exchanger (8) again in the reverse direction. During
this process, it again goes over into the super-critical state due
to the increase in temperature and accordingly enters the
separation apparatus (1) through the pipe (3). In the figure, the
conditions are slightly simplified in that a 100% heat exchange in
the heat exchangers (8) and (14) is, of course, not possible. A
certain amount of additional cooling of the gas stream to be
liquefied will usually be necessary after the gas has passed
through the heat exchanger (14) and consequently also slight
additional heating of the returned gas stream after it has passed
through the exchanger (8). However, this additional heating and
cooling involves only the extremely small quantities of energy
which are lost. According to the flow diagram in the figure, the
distillation residues to be separated is continuously supplied to
the separation apparatus at (2) through the pump (16) and the
heating coil (17) which together with the reducing valve (9) and
intermediate container (10) are accommodated in the same heating
bath (18). Here again, an additional heating stage, not shown in
the drawing, can be interposed in series. The quantities of carrier
gas which are still present in the products collected in the
storage containers (7) and (12) and which escape during the release
of pressure are liquefied by the compressor (19) and carried to the
input end of the pump (15).
In a special experimental procedure, the charging and separation
apparatus (1) consists of two iron pipes of about 5 cm internal
width and 1 m length which, as shown in the figure, are welded into
a spherical container at an angle of about 120.degree.. The upper,
bent pipe is filled at the top with filling bodies 4 mm in
diameter, at the bend with balls of 1 cm in diameter and lastly, at
the opening into the spherical part, it is provided with the baffle
plates shown in section. The spherical separation part consists of
two flanged dishes welded together and is filled with balls of 1 cm
in diameter above the perforated plate arranged in the middle. The
charging stage is carried out with propane as carrier gas at an
operating temperature of 120.degree. to 130.degree. C. and
pressures between 90 and 150 atmospheres. During the discharging
stage, the pressure is reduced to 30 to 35 atmospheres so that the
discharged propane can still be liquefied above room temperature.
The volumetric capacity of the whole separation apparatus (1) is
about 5 liters. Under these conditions, 25 to 50 liters of
distillation residue can be separated per hour into asphalt and
high boiling petroleum constituents. The higher the pressure, the
more extensive is the separation.
It is especially in this last property of the products of the
process that the new process has a great importance for the working
up of residues form petroleum distillation. It is known that
vanadium compounds are extremely undesirable in the products of the
process because they can not only interfere with further working up
but above all can give rise to severe corrosion during the
combustion of the hydrocarbon compounds. The conventional working
up processes therefore contain a special stage for the removal of
vanadium. According to the invention, this is not necessary.
The separated petroleum constituents are largely ash-free and
contain only traces of vanadium compounds.
* * * * *